I. Field of the Invention
The present invention relates to instruments which measure surface finish appearance parameters of highly reflective surfaces such as automobile paint finishes.
II. Description of the Related Art
Smooth, highly reflective surfaces are found on many articles of manufacture because of their cosmetic appeal. Measurement of the perceived quality of appearance of such surfaces is highly desirable to enable setting and maintaining standards and to enable detection of small changes for the purpose of evaluating and improving the processes and materials used to make those surfaces.
Glossmeter Limitations:
Glossmeters, which measure the amount of light reflected off a surface, have been adequate for measuring surface finish parameters of surfaces such as concrete, rubber and wood which are minimally reflective. Glossmeters are also useful on moderately reflective surfaces such as file cabinets, other office furniture and Formica.TM.. However, glossmeters are not sufficiently able to discriminate the levels of surface finish quality perceived by people on highly reflective surfaces such as the Class A finishes on the exterior body panels of automobiles. Because of this limitation, glossmeters are rarely if ever used by automotive dealerships, body shops, detailers or even by field representatives of refinish paint manufacturers.
One of the leading manufacturers of glossmeters, BYK-Gardner, makes a device called Micro-Haze which has added a second reflection haze scale to supplement its specular gloss readings. The device produces a beam of light which is reflected of the surface being measured, goes through an aperture and falls on photoelectric sensors. The gloss value is dependent on the input of sensors receiving light at a specular reflection angle from 19.1 to 20.9 degrees. The haze value is dependent on the light reflected at 1.8 degree range on both sides of the gloss angle. The outputs of its detectors are processed electronically to produce a reading from 1-180 gloss units on its own gloss scale and from 10-500 units on its Haze scale. The light received by an additional detector at a 45 degree angle can be used to perform a mathematical compensation on the haze value for variances in brightness levels.
Micro-Haze currently costs over $5,000 and is rarely if ever seen at body shops, dealerships, detailers or reconditioning centers. Micro-Haze provides more information about surface finish quality than glossmeters which do not produce haze measurement, but it is limited in its ability to measure what humans perceive when they are evaluating surface finish quality. BYK-Gardner's application literature states "The measurement of specular gloss and reflection haze does not take into account the visual impression of orange peel."
Visual-mechanical Devices:
Early attempts to measure the quality of appearance of surface finishes used a device known as the Glow Box.TM.. This device is comprised of a metal light box, approximated 12 inches square, with bulbs inside and with four external supporting legs. A test object printed with ten rows of "C" shaped Landolt rings, each row a different height, is affixed to the underside of light of light box and the light box is then set on its legs on a reflective surface. The user moves around the Glow Box looking at the reflection of the test object to determine which row has the smallest "C" shaped rings that don't appear as a closed circle. Ambient light also reflects off the surface being measured and therefore the Glow Box can only be used in darkened rooms and it can't be used outside during daylight. Furthermore, neither the angle with which the viewer sees the reflection, nor the distance the user is from the surface is controlled. Repeatability therefore can be a problem. The Glow Box is neither small, nor portable; it requires 120-volt power for the light source.
The present invention can be used outside or inside under any lighting conditions; the Glow Box cannot. In addition the present invention reflects light off the surface at a fixed angle while the Glow Box angle of reflection can change from minute to minute or from user to user. The present invention is battery powered enabling it to be used in the field. The Glow Box requires a 120 v power cord. The present invention has a compact, lightweight plastic enclosure which is easy to transport and store, and is less likely to damage high quality painted surfaces during normal use if dropped. In comparison, the Glow Box is a 12 inch by 12 inch metal box supported by four metal legs.
Japanese automotive manufacturers are reported to have used a PGD meter at one time for evaluating finish quality. The PGD meter is a relatively complicated and expensive instrument. It employs an optical system which bounces light off four internal mirrors and requires magnification in the viewing tube. Its operation further requires a variable resistor and voltmeter to keep the light source in a limited range of illumination. Another serious drawback is its use of a 55-degree angle of reflection. Angles of that magnitude are primarily suitable for finishes with low to moderate reflective qualities and are not sufficiently discriminating with highly reflective finishes.
The present invention is considerably less expensive and less complicated than the PGD meter which has four internal mirrors and a magnifying eyepiece. The present invention has no mirrors, no magnification, and no eyepiece. The PGD meter is limited to monocular vision; the present invention has the preferable binocular vision. The PGD meter uses a 55 degree reflection angle. The 20 degree angle of the preferred embodiment of the present invention is much better suited to measurements on highly reflective surfaces.
A Tension instrument was tested by at least two paint manufacturers in the past for its ability to evaluating highly reflective finishes on automobiles but is not commonly in use in the US today. Tension employs a test object comprised of a grid pattern in which the lines become progressively smaller and closer together. It is a large instrument which has a viewing port designed to hold an instant developing film camera to take a photograph of the test object's reflection on the surface being measured. After the photograph of the reflection is taken, the photograph is examined to determine the smallest lines which can be discerned as being visually distinct from each other. The number assigned to the smallest visible lines is the measurement value.
A disadvantage of Tension is that the resolution and consistency of instant developing film is relatively poor and that affects repeatability and reproducibility. The cost and problems associated with instant developing film are therefore another disadvantage. One paint manufacturer found it necessary to use only fresh film bought directly in case lots from the manufacturer. Tension is not a commonly used instrument in the automotive refinish industry and is seldom if ever seen in the automotive field testing.
The Tension meter requires the use and expense of an instant developing camera and film. The present invention requires no camera, no film, and no subsequent manual measurements and calculation. In addition, the preferred embodiment of present invention uses a test object which is far more discriminating than the linear grid pattern used in Tension.
Electro-optical Devices:
Although the above referenced prior art has not solved the problem of adequate field measuring of the quality of surface finish, the need for measurement of this parameter by automobile manufacturers is very strong. Currently expensive electronic instruments made by ATI and Autospect are in use in automotive factories in the US.
One of the earliest electro-optical instruments designed to measure appearance quality of surface finishes was the Hunter Dorigon instrument. A light source produced a beam of light which is reflected of the surface being measured to an optical sensor at a 30 degree specular angle. A slit was positioned 3/10ths of a degree from the 30 degree position. The amount of light it received at these two locations was compared and processed by a computer to produce a numerical value. The Hunter Dorigon instrument is large, complex, and costly. It is rarely if ever used outside of laboratory applications and it is no longer being produced or serviced by Hunter.
ATI's Model 1864 SQC Portable Appearance Data Collector costs approximately $16,000. ATI's sales brochure describes its operation as follows: "During operation, a controlled beam of light is projected through an opening onto the test specimen. The reflected portion of the light beam passes through a rotating eight bladed disc and is focused upon the lens at the aperture. As the blades pass through the light beam, the silhouetted image of the blades moves across the detector slit causing a large increase in light flux to be present at the photo detector. This detector converts the light to an electronic signal that is later processed by a microprocessor and is displayed in D.O.I./Gloss values."
Autospect's QMS-BP Quality Measurement System is even larger then ATI's 1864 system. The system includes a high gloss sensor, a low gloss sensor, a processor, a battery charger, VGA monitor, keyboard, printer, three batteries and an AC power module. It uses a complex photoelectric system and microprocessor to covert reflected light to its own 0 to 100 scale.
Autospect's QMS-I system has an inspection arch mounted over an automobile assemble line. As a vehicle passes through the arch, information is acquired from the plant's network regarding the VIN, color, style etc. Autospect sales literature states: "At predetermined positions, the cameras take pictures of the light reflected from the vehicle's surface. The images are digitized and analyzed by Autospect's specialized software. "
The high price and complexity alone are enough to preclude the prior art electronic surface finish appearance instruments from being used by automotive dealerships, detailers and body shops. In addition, there is growing concern that the measurement numbers produced by even the most expensive and complex surface finish appearance instruments may not correlate well with human perception of the quality of appearance of high gloss surfaces. The ASTM, American Society for Testing and Materials, has formed a sub-committee to examine the psycho-physics of human perception of surface finish quality in order to develop methodology and measurements in this field which accurately correlate with human perception.
In spite of the strong economic need to measure the appearance quality of highly reflective surface finishes such as on automotive exterior body panels, the prior art, including both visual-mechanical and electro-optical, has not produced a relatively low-cost instrument which satisfies this need. This is evident by the fact that instruments for measuring finish appearance quality are virtually unknown at automotive dealerships, body shops, and detailers.
The present invention overcomes all the limitations of the prior art. The present invention not only costs considerably less than glossmeters, it measures "distinction of image-gloss" which more closely correlates to human perception of finish appearance quality on highly reflective surfaces.